Radio receiving circuits



LSGSAOQ June 14, 1932 T, K|NMAN RADIO RECEIVING CIRCUITS Filed Sept. 12. 192' 2 Sheets-Sheet Inventor: Thomas H.KLnman, by M HLS Attorney.

RADIO RECEIVING CIRCUITS Filed Sept. 12, 1927 2 sheets-Sheet 2 IA A. Lg. h

ThOmas Hl'flnman,

L'Il

Patented June 14, 1932 UITED STATES PATENT OFFICE THOMAS H. KINMAN, OF BILTON, NEAR RUGBY, ENGLAND, ASSIGNOR TO GENERAL ELECTRIC COIvIPANY, A CORPORATION OF NEW YORK RADIO RECEIVING CIRCUITS Application filed September 12, 1927, Serial No. 219,083, and in Great Britain September 14, 1926.

The present invention relates to radio receiving circuits, and more particularly to a receiving circuit which is adapted selectively to receive in turn signals of a plurality of different wave lengths.

In a receiver of this kind, when used within a certain radius of a station transmitting at one of the wave lengths which the receiver is adapted to receive, interference is frequently experienced when receiving on another wave length, even if the latter differs considerably from that used by the station situated near to the receiver, and it is the object of the present invention to eliminate, as far as possible, this interference.

According to the invention, the receiving system includes a plurality of tuned input circuits, means being provided whereby one or more of the said circuits may be utilized alternativeiy either as a receiving circuit, or as rejector circuit. The tuned circuits are usually associated either inductively or directly with the aerial or like circuit, and I preferably employ a switching arrangement whereby one of the tuned circuits can be disconnected from the aerial circuit when reception on the wave length to which that circuit is tuned is not desired, and to connect that circuit in the aerial circuit so that it forms a rejector circuit when reception on another wave length is desired. The rejector circuit thereby prevents interference from occurring, due to the transmitting station operating'at the wave length to which the rejector circuit is tuned.

In one form of receiving arrangement embodying the invention, the aerial-earth circuit contains two tuned circuits in series, each of which is tuned to one of the wave lengths it is desired to receive. A switch is arranged to connect the aerial circuit in the desired manner to the input circuit of a valve or other arrangement for detecting the received impulses. In one position of the switch, one of the tuned circuits is short-circuited, while the other circuit is connected across the grid and filament of the valve. In the other positi on of the switch, the tuned circuit, which in the first position was short-circuited, is connected across the grid-filament circuit of the valve, while the other tuned circuit remains in ser es in the aerial circuit.

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response is given by one tuned circuit, while a minimum response is given by the other tuned circuit, which, nevertheless, functions to absorb signal energy of the frequency to. which it is tuned, so as to eliminate interference from that frequency.

A switch is provided as before so that the function of the circuits as receptor or rejector circuits can be reversed. In order that the signal response shall be a maximum for one circuit, and a minimum for the other, it is necessary to connect the detecting device, (when this is voltage operated), across the inductive portion only of the tuned circuits. In this way, the capacitive portions of these circuits are so connected that the circuit not in use for receiving purposes functions as a rejector circuit, and gives a minimum signal response in the detector.

In a case where one or both of the tuned circuits consists of inductance in parallel with capacity, it is necessary to connect the circuits through a capacity, and sometimes also through an inductance, the purpose of which is to prevent the tuning of one circuit affecting the tuning of the other circuit.

usual reaction coil can be included, a variable coupling being provided between the reaction coil and the tuned circuits. The tuned circuits, however, must be sutiiciently removed or screened from one another to avoid interaction between the two circuits.

It is important that the inductance and capacity. variation. of the tuned circuits should he correctlyiproportioned. and; related to one another in order to avoid undesirable interaction, and, where parallel circuit arrange- *ments" are employed, precautions must"he taken to prevent appreciable shunting ofenergy from one circuit to the other.

In order that the invention may be fully' understood, reference isdirected to theaccompanying drawings, wherein Figs. 1 to 3 relatesto'emhodirments ofmy inventi'on which are of particular-utility when. the receiver is situated: near: one-transmitting. station and at-a distance from another transmitting. station; .and- Figs; tt'o 9 relate to. further modifications of my invention.

Referring to; the accompanying drawings, Fig.1, thereof shows a receivingsarrangement inaccordance with the invention,- in which the aerialeeart'hz' circuit AE contains :two' tuned circuits QL C -v andL C inseries,each of which is rtunedtoonerot thewavelengths it is desirede-to-receivet- A switch S is arranged to connect the aerialcircuit in the desired mannerrto the input circuit of a valveV or other arrangement for detecti-ngthe 2 received impulses. lnqpos-iti'on- (1%) oi-the switch, the tunedr-circuit L 0 is short-circuited, while the other tuned circuit; L G is connected across the gridfiand ifil'ainent of the-valve. Inposition (-2).-of the switch the-tuned circuit L 0 whichimthe firstposition was short-circuited, is connected across the gridfilament circuit of the .va-lve, while the other tuned circuit -L' C remains in series in. the aeriaLcircuit. 1

In. operatingthereceiver,- the switch S is firsti put;in.2position-.(2). in which the more distant station islto be-received,-=i.. e., the cir-. cuit L C which in position( 1,) is short-circuited,.is tunedin the rusual manner. Interference from the local..station eisthen-.suppressed by tuningthe other circuit L 0 which. is in series with' the aerial, sosthat it acts: as a rejectorr. :to the? undesired signal. Upon the switch, bei-ngithrown to the alternativeposition (1) the-rejector circuit L C whichhas alreadyibeen tuned to the local !or interfering; station, .is connected f in. circuit for reception, whilst the other tuned. circuit L C is short-circuited...

The .factthat. the resonant. value ofithe rejector circuitis slightly different vwhen it is usedior. reception is not important as the tuningofthis circuit in any caserwill not-be critical It will, of course, be obivousthat the two tuned; circuits 1 may be interchanged, so that eithenmay function .asathe. .rej ector circuit.

Referring to :Fig. 2 in which a modified form of Fig. 1 is shown, the circuit L G functioning as a rejector circuit is included in the input circuit oi the valve V, instead of in the aerial circuit, and in addition to this modification a compensating condenser K is included across the circuit L C when it acts as a rejector-circuit, the value of the condenser K being adjusted so that the resonant frequency of the tuned circuit is the same whenit actseither as'the tuned input circuit, or as the rejector circuit. When it acts as a rejector circuit, the additional condenser compensates for the natural capacity ofthe aerial, which is removed when receiv- 1ng on the alternative wave length. If desired, an additional.i-nductance'may he used in conjunction with the compensating. condenser. I

Iii-Fig: 8 the two-tunedcircuits-L G and L G: are coupled to separate-aerial coupling inductances -La and La respectively arranged-*in-series. The switch S connects either. tuned circuit tothe'valve input circuitaccording, to which wave lengths it. is desired to receive, the remaining tuned circuit functioning: as a rejectorz circuit. Where the two wave lengths are not very widely separated each tuned circuit acts as a rejector lDElLUIDEY- Inthis arrangeemnt; the aerial cou pling inductances La and La maybe made small-and the tuning inductances L and. L large and a 'more. selective circuit results.

Thev-alues of'th'e'aer-ialtcoupling inductances must he so chosen thatsthe impedanceot the aerial circuit: is suitable for either wave length when both inductancesare incircuit. As previously. described, the inductances must be-separated s0 as toprevent interaction.

The arrangements hereinbefore set forth are of particular-- use when therccciver is situated near one-transmitting station, and at a distance from another transmitting station, and difiiculties are experienced in receiving the distantstation, owing. to interference-fromthe near station. However, the arrangements arealso of use when the signals-receivedfrom thetwo stations are: of approximately equal strength, and thetwo wave lengths are not widely separated.-

Referring to Figw l, the tuned circuits L 0 andL C each consist-0f aninductance in series-witha capacity, and are arranged in parallelto one another in a-common aerialearth circuit AE. Thermionic valve V is arranged for the purpose-either of amplifyingor detectingthe received oscillations, and the grid of-V is connected througha switch S to-eithe-r of the two tuned circuits,- as shown.

The-gridrircuit. of valve-V is adapted to be connected across thatpart of .one, or other, of. the tuned circuits, which gives the greatest signal response, while, at the'same time, the action is such-that for the other tuned. circuit,.a minimum. signal:respon'se is obtained:

It is assumed that the valve V is voltageoperated, and the grid circuit is connected across either of the inductances L or L in positions 1 and 2 of switch S. L Cl is tuned to one frequency, while L G is tuned to another, which may be a neighboring frequency. In position 1, oscillations of the frequency to which L C is tuned are impressed on the grid circuit of V, whilst the oscillations which occur in L C do not affect the grid circuit and consequently L G: acts as a re jector circuit to eliminate interference. In position 2 of switch S the functions of the circuits are reversed.

In Fig. 5 a modification of Fig. 4 is shown, in which L G are arranged in parallel to one another, while L 0 remain series-tuned. In this case, it is necessary to employ condenser K connected between the tuned circuits, the value of which is so adjusted that tuning either of the circuits L 0 or L CZ will not materially affect the other. In this arrangement is also shown a reaction coil L,., which may be coupled to either of the inductances L or L in well-known manner. If desired, two separate reaction coils can be employed.

Fig. 6 shows a modification, in which both the tuned circuits consist of inductances L L in parallel with capacities G C Interaction between the two tuned circuits is prevented by means of the inductance L and the capacity K, connected as shown between the two tuned circuits and the aerial A. If desired, the circuit LK can be tuned to a third wave length, and may act in a similar manner to the other tuned circuit in serving either as a receptor or rejector circuit to this third wave length. As shown, switch S is provided with three positions whereby any of the three tuned circuits can be connected across the input circuit of valve V. The arrangement can therefore be operated on one of three wave lengths, as desired, by means of switch S. In this case, it is necessary to tune circuit L C to the highest frequency, LK to the intermediate frequency, and L 0 to the lowest frequency.

If the third wave length is not required to be received or eliminated, in this arrange ment the lower and higher frequencies must be tuned in by circuits L G and L 6 respectively. The inductance L and condenser K then serve effectively as radio frequency impedances to the higher and lower frequencies respectively.

In Fig. 7 is shown an arrangement where additional selectivity is required due to the interference emanating from a local station and to the proximity of the two wave lengths.

" one side of the condenser C through another condenser K to the high potential end of the coil L It will be seen that oscillations set up in the aerial circuit L C will be induced in the other circuit L C by virtue of the coupling and connections of the two circuits, which will cancel out the E. M. F. normally impressed between the points marked X and Y.

To prevent the balancing process materially reducing the strength of the weaker signal, the modification shown in Fig. 8 is used. Athird circuit L C is connected directly across the input terminals of the detecting device X, Y, and is tuned to the same wave length as the aerial circuit L 0 toreceive the weaker signal. 7

It will be seen that there are two coupling points between the aerial circuit and input circuit, one through the condenser K, and the other through the circuit L G by virtue of the coupling between L and L It can be arranged in. practice for one of these paths to offer a much higher impedance to the weaker or unbalanced signal than the other, so that it is impressed upon the detecting or amplifying device at practically normal strength.

In Fig. 9 is shown an arrangement similar to that illustrated by Figs. 1 to 3, but

modified to enable closely adjacent frequencies to be received alternately. In this case, a compromise is effected between a series and parallel arrangement of the two tuned circuits by including a part only of the inductances L and L in the aerial circuit. The arrangement, however, is similar to the arrangements hereinbefore described, in that neither of the tuned circuits are shortcircuited-by the switch in either of its two positions. I

While, in general, the invention has been described in its application to the reception on two alternative wave lengths, the possibility of modifying the arrangements illustrated so as to render them suitable for the reception on more than two wave-lengths, the circuits not in use for reception serving to absorb or reject the undesired signals, should not be overlooked, and it is intended that the claims hereof should be construed with this possibility in View.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a radio receiving system, a plurality of tuned input circuits and means whereby at least one of the said circuits may be utilized alternatively as a receiver or a rejector circuit.

2. In a radio receiving system, an input circuit, a plurality of tunedcircuits coupled to said circuit, and a switching arrangement whereby one of said tuned circuits may be connected in said circuit so as to function alternatively as either a receiving circuit for the system or a rejecting circuit for the frequeneyito which: another of said cuitsiisiresponsivev 3. "A radio "receiving-apparatus comprising an acrialicircuitga plurality of'tuned'circuits coupled to said aerial circuit'and each tuned to one of the Wave lengths it is desired to'refceiv'e,1a:sWitchingJdevice for connecting one of said circuits so that it functions as a receiving circuit for the wavelength towhich it is'tuned while'an'othenof said'tunedcircuits-fu'nctions as a rejecting circuit'for said wavelength and for alteringthe connections tuned cir= so that the functions of said tune'd' circuits I are reversed.

l. In a radio receiving system, an" aerial circuit, two circuits each'tui'iedto a different frequency and associated with said aerial circuit, an electrical" valve, and 'means' I for connecting-said valve to said tuned circuits so that a maximum signal response is given to said valve by one tuned'circuit While a minimum" response" is given by thegother tuned'circuitwhich functions to absorb signal 'energyof thefrequency to which it- 1S tuned thereby s'ub'stantially 'to-eliminate interfe-renc'e from that frequency, said means being arranged to change the connections-between said'va'lve' andsaid tuned circuits in such a manner'that the 'functions of the two circuits areireversed'." 4 v T 5-. A circuitii'arran gement for receiving radio signals on alternative Wa-ve lengths comprising. an aerial 'system,- a plurality of circuits ea'ch tuned to one 'of the desired Wave lengths and coupled to said system, an electrical va'lve" provided witlfinput terminals, rand a'switc'h arranged to connect said input terminals to-said aerial system so that in 'onepositionof the'switch'a maximum signal response is given by one tunedfcircu'it While-1a inin'ini'u'ni signal response is given by th'e other tun'ed circuit, and in another position of the: switch the connections are such asftoreverse' the functions of the tuned circuits.

6. A radio receiving arrangement including 'a' receiving device, an' aerial circuit which contains two tuned" circuits connected in series, and a switch arranged in one position to short circuit one of said tuned circuits and connect the'other' circuit to said receiving device, and in the other'position to remove the short circuit and connect-both of said circuitsto the receiving device.

7:111" aradio receiving system,a plurality of tunedinput circuits; means Wlierebyone of said circuits may be utilized alternatively as a receiver and a rejector circuit, and compensating unea-ns arranged to be connected across one of said tuned circuits.

In witness'whereof, I have hereunto set my hand this 24th day of August, l927-.

THQMAS H. KINMAN. Y 

